1. Field of the Art
Embodiments of the present invention generally relate to surgically implanted eye prostheses, in particular, to microfabricated, fluid-filled intraocular lens devices.
2. Description of the Related Art
Surgical Procedure
An intraocular lens (IOL) can be used to replace a natural crystalline lens in human patients. Surgically replacing the crystalline lens includes making a main incision of approximately 2 to 4 millimeters (mm) in the periphery of the patient's cornea, cutting a 5.5 to 6 mm diameter circular hole in the eye's anterior capsule surrounding the lens, and removing the lens with phacoemulsification.
Because replacing the crystalline lens with an intraocular lens is an invasive procedure, this option is reserved for when vision is significantly impaired. Most commonly, it is used when the lens has become cataracted.
However, several factors are making this a less invasive procedure with faster recovery times. These include the trend of using smaller surgical instrumentation with a correspondingly smaller main incision to reduce postoperative recovery time and astigmatism. Furthermore, femtosecond pulse lasers are beginning to be used for lens/cataract removal, which makes the procedure safer, faster, and more accurate.
Surgical Complications
The most common surgical complication of lens replacement is posterior capsular opacification (PCO), which occurs when residual lens epithelial cells move to the posterior portion of the capsule and proliferate. This makes the capsule hazy and creates visual disturbances. PCO is treated by externally using a neodymium-doped yttrium aluminium garnet (Nd:YAG) laser to remove a section of the posterior capsule. It may also be alleviated by cutting the posterior lens capsule with a femtosecond laser.
Intraocular lenses are often designed with a square edge to prevent lens epithelial cells from migrating to the posterior capsule, and therefore prevents PCO.
Similar to posterior capsular opacification, anterior capsular opacification can also cause contraction of the lens capsule and visual opacification.
Accommodation and Presbyopia
“Accommodation” is where an eye changes optical power to focus on an object. This occurs from contraction of a ciliary muscle, which releases tension on the lens capsule. Upon release of this tension, the human lens naturally bulges out, increasing optical power.
Presbyopia is a clinical condition in which the eye can no longer focus on near objects. It is believed that this is a multifactorial process caused primarily by a loss of elasticity of the human lens. Therefore, replacing the human lens with an accommodating intraocular lens provides the capability to restore focusing ability and cure presbyopia.
Existing Devices
Current intraocular lenses can be categorized into three categories: monofocal, multifocal, and accommodating.
Monofocal lenses provide a single focal distance. Therefore, patients with a monofocal intraocular lens can no longer focus their eyes. This makes it difficult to focus on near objects.
To alleviate this condition, multifocal intraocular lenses were developed. Multifocal intraocular lenses provide simultaneous focus at both near and far distances. However, because of the unique optical design, patients may have a loss of sharpness of vision even when glasses are used. Patients can also experience visual disturbances such as halos or glare.
Accommodating intraocular lenses use the natural focusing ability of the eye to change the power of the intraocular lens. There are many designs of accommodating intraocular lenses, including single optics that translate along the visual axis of the eye to focus, dual optics that move two lenses closer and further apart, and curvature-changing lenses that change focal power by changing the curvature of the lens.
Future Market
Less invasive and faster surgical procedures in conjunction with accommodating intraocular lenses may allow intraocular lenses to be used for wider applications than are currently used today. This includes treatments for cataracts as well as presbyopia. This is a much larger market because almost all individuals undergo presbyopia around the fourth decade of life.